I have seen several WM maps with mountain ranges like these but I have not yet figured out how to make them. Can someone give some hints as to how to make mountain ranges like these? They look like fingers with long valleys and ridges.

That real-world example is defined by heavy erosion of a relatively featureless mountain uplift (orogeny). You may or may not be able to reproduce the effect in WM directly at the final scale you want. You may have to do your WM modeling at a larger scale for the WM erosion node to give comparable results, then scale the results down afterward.